Ageing fibreglass hull?

[JumbleDuck]

Yes this was my point, the keel usually attaches to the hull, not the grid. The grid is literally just glued to the hull for rigidity, and sometimes that glue fails under load. The GRP though is usually fine unless it's had a spectacularly hard knock.

Generally speaking the keel is bolted through both hull and grid. The hull is relatively flimsy (like all monocoques) and so takes very little of the load at the point of connection: the forces are spread out by and across the whole grid. Some notes on the issues this raises at https://assets.publishing.service.g...t_data/file/810291/MGN_XXX_Keel_Grounding.pdf. It's not just repair that's problematic; it's almost impossible to do a really good inspection.

Edit: Just found this interesting comment from Pantaenius:

 

[Graham376]

For an idea of what can happen when the grid is only held to the hull by filler, have a look at Expedition Evan's videos on Youtube.

Edit - As can be seen in this one, the keel bolts don't pass through the grid - (112) Our SALVAGE SAILBOAT Has Been Leaking for Years | Expedition Evans 6 - YouTube

 

[lustyd]

@JD I've never seen one bolted through both but willing to take your word for it. Certainly the Expedition Evans boat was not, and neither is mine. Both Groupe Beneteau but different makes and very different years/sizes, suggesting that GB generally bolt to the hull only. That's quite a significant proportion of boats out there so I would have to disagree with the "generally speaking" part of your comment!

 

[Ship'sCat]

Almost certainly they will be stainless steel. As suggested earlier, the weakness of this type of attachment is the sealer failing allowing damp to get in and cause crevice corrosion of the shanks. You only normally find out when they break although sometimes you might see rust weeping out from under the plate.

GRP is in itself not particularly strong or stiff. It gets its strength in boats partly from the shape and partly from the stiffening added (bulkheads, stringers etc.). Interested in what breaking up was "better than", although guess it would be steel first followed by wood which is difficult because a wooden boat is a web of interlocked small pieces of wood held together with a myriad of fastenings!

I think if we check the article the breaker is comparing old grp with new grp.

 

[Refueler]

@JD I've never seen one bolted through both but willing to take your word for it. Certainly the Expedition Evans boat was not, and neither is mine. Both Groupe Beneteau but different makes and very different years/sizes, suggesting that GB generally bolt to the hull only. That's quite a significant proportion of boats out there so I would have to disagree with the "generally speaking" part of your comment!

Some boats had a 'cats cradle' like form laid into the 'green' hull during production. The 'cats cradle' being like a central spine running longitudinally with legs going off at 90 deg following the transverse curve of lower hull. The Keel bolts later then passed through both hull and spine if Fin ... through hull and respective legs if bilge keel.
The idea being to spread the load via the form into the hull.
Unfortunately some suffered because of the manner of fastening the keels using penny washers to spread the load into the form. This when grounding or hitting obstruction could cause damage not only to the hull but 'cradle' as well.
A terrible setup to inspect after such event.

A variation on the above was used by some such as RIDAS in Tallinn ... their 35 being a prime example. I was present - just put my race boat alongside when Ridas invited me to look at a 35 they were lifting out (Pirita Marina) ...
In Tallinn bay - there is an infamous concrete block sits waiting daft sods who try to sail over it ... the block is there from Soviet time when Subs would come in .. lay submerged alongside it while refueling by underwater pipeline from Milstrand Terminal ...
This 35 had hit the block at an estimated 7kts.

35 lifted and guys then proceeded to measure the offset this hit had caused .. by eye - she looked straight .. but measurements showed a degree or so ..
The 35 has a 'cradle' and bolts that come up through - BUT instead of solid GRP surround - the 'hole' is oversized. The bolt comes up through hull and cradle surrounded by Sikaflex allowed to cure and then bolted up.
Simple but effective shock absorbing way to fix a keel.
In Ridas own words - he reckoned without that format - that boat could have suffered serious hull to keel damage. As it was - there was no damage at all to the hull or cradle. They dropped keel .. removed old Sika .. re-bedded and bolted up.

 

[Tranona]

As I said, yes. And as I said previously, over time the issue is going to be the impossibility of knowing which boats have thumped something and which haven't. Unthumped, the design is fine.

This is worth looking at bavariayacht.org/forum/index.php/topic,3198.0.html The boat is a Vision 46 which has a glued in grid. As you can see the visible damage is actually in the GRP moulding that forms the grid. If you read through you will find that the seller eventually owned up to a grounding.

Of course further investigation is required to see what else is damaged, but the poster quite rightly walked away even though the boat was exactly what he wanted.

Over the years we have seen a number examples of Bavarias that have grounded, either in the flesh or posted on the forum. Most for obvious reasons are the type with glassed in grids, just as used by most production builders in the same period. Almost always the 3 visible signs are front of the keel detached or sealant broken, depression of the hull aft of the keel and cracks in the grid mouldings usually at the after end in front of the engine, under the chart table and galley. Sometimes there are cracks in all the grid members the length of the keel usually when the boat has dropped straight on the keel.

So, I think it is relatively easy to see the first signs of damage, but what is less easy is going further and looking at the attachment of the grid away from the immediate vicinity of the keel. This is true of both tabbed and glued grids, except that failed tabbing is easier to spot and perhaps repair.

There is nothing new in the problems related to dealing with damage from grounding. From the 70's onwards when fin keels became common attached to GRP canoe bodies, grounding, particularly when racing has resulted in extensive damage to internal structures. Any Solent based repair yard will have had a steady stream of such repairs. Why it has become more visible now is perhaps because of the vastly increased numbers of fin keel boats, coupled with draft increases of 30-40%. When you mix deep draft boats with competitive sailing, thin water, hard seabeds and wilful tides you get damaged boats. Add in a bit of crap navigation and similar things happen even without the competitive element. Meanwhile the other 99% of owners of fin keeled boats happily go on their way wondering what all the fuss is about.

 

[Refueler]

It is not actually a new thing anyway as many Westerly Centaur / Berwick etc. can tell you.
The addition of rovings to keel areas of those boats was a steady biz for many yards. One of the contributory factors was the splayed angle of the bilge keels causing serious stress to the keel to hull areas on drying out moorings ... hard standings etc.

 

[JumbleDuck]

This is worth looking at bavariayacht.org/forum/index.php/topic,3198.0.html The boat is a Vision 46 which has a glued in grid. As you can see the visible damage is actually in the GRP moulding that forms the grid. If you read through you will find that the seller eventually owned up to a grounding.

Yikes. That's pretty dreadful.

Of course further investigation is required to see what else is damaged, but the poster quite rightly walked away even though the boat was exactly what he wanted.

Over the years we have seen a number examples of Bavarias that have grounded, either in the flesh or posted on the forum.

Te trouble, with all due respect, that only the visible damage gets ... um, seen. Of course it may be that the design is cunning enough to include a bildge liners as a sort of telltale which breaks (just) before any serious structural damage occurs but that may be a bit subtle and/or difficult to achieve. So who knows how many boats, and which boats, are sailing around with significant but hidden structural damage? This sort of thing is much better known in the glider world, because every time a particular model reaches a set life the manufacturers buy one and very carefully dismantle it - wrecking it in the process, of course - to examine every part of the structure. Perhaps that will be worth doing to yachts if they ever start failing in significant numbers.

There is nothing new in the problems related to dealing with damage from grounding. From the 70's onwards when fin keels became common attached to GRP canoe bodies, grounding, particularly when racing has resulted in extensive damage to internal structures.

Yes, but (see the MCGA report I linked to) the issue with bonded-grid hulls is not that they fail or that repair is expensive. Both of these are, as you say, long term issues. The problem is now that it can be very difficult to tell whether damage has in fact occurred.

Another gliding example. Sorry. The Olympia 463 (I hope I have the number right) was a lovely British-made glider which used an wood-aluminium composite main spar. One of them crashed, fatally I think, and it was discovered that (a) the glue between the wood and the metal had failed and (b) there was absolutely no non-destructive test which could tell whether this affected any particular example. So the entire class were grounded, permanently, and the friend I knew who had one gave it away as a static display piece.

So, back to sailing: An unbonded, or partially unbonded, grid looks just like a bonded one. So to repeat, my long term worry is not that modern boats are going to fall apart, but that it will become increasing difficult to tell whether they have been structurally compromised or not.

But just to be clear: I see no reason to believe that GRP loses any strength in regular service and I am sure that moderns designs are quite strong enough for all the loads in regular service.

 

[JumbleDuck]

It is not actually a new thing anyway as many Westerly Centaur / Berwick etc. can tell you.
The addition of rovings to keel areas of those boats was a steady biz for many yards. One of the contributory factors was the splayed angle of the bilge keels causing serious stress to the keel to hull areas on drying out moorings ... hard standings etc.

I spent two weeks of what now seems like my youth building 5m of stainless strip, 20 litres of polyester resin, 5 litres of epoxy resin and an awful lot of glass fibre into the hull of what later became my Westerly Jouster to beef up Laurent Giles' hopelessly optimistic ideas of how to attach a keel. They seemed to think that thickening the layup from 14/" to 3/8" for an inch or so around the slight recess into which the flange at the top of the keel fitted would be enough.

 

[Refueler]

I spent two weeks of what now seems like my youth building 5m of stainless strip, 20 litres of polyester resin, 5 litres of epoxy resin and an awful lot of glass fibre into the hull of what later became my Westerly Jouster to beef up Laurent Giles' hopelessly optimistic ideas of how to attach a keel. They seemed to think that thickening the layup from 14/" to 3/8" for an inch or so around the slight recess into which the flange at the top of the keel fitted would be enough.

I got tired of checking out Centaurs / Berwicks / Konsorts etc. to see if the work had been done ..

So many I saw were bodge DIY jobs and a number had to be cleared and redone. An awful job that gladly - yard guys did ...

I have two pet hates on boats like this ..... keel strengthening and headlinings ! Lucky the Sunrider I have has a substantial bilge keel deal and it would take a big bomb to do anything to them. But my headlining has dropped and I'm dreading the job ..

 

[Graham376]

I got tired of checking out Centaurs / Berwicks / Konsorts etc. to see if the work had been done ..

I had to repair the keel stubs on our Berwick but the big difference is that owners knew about the problem and kept an eye open, stress cracks and flexing were easy to see. OTOH the damage to a grid system is often hidden and the modern high aspect keels with small mounting area aren't designed to take the ground, unlike older designs which were more forgiving when abused.

 

[Tranona]

Yikes. That's pretty dreadful.

Te trouble, with all due respect, that only the visible damage gets ... um, seen. Of course it may be that the design is cunning enough to include a bildge liners as a sort of telltale which breaks (just) before any serious structural damage occurs but that may be a bit subtle and/or difficult to achieve. So who knows how many boats, and which boats, are sailing around with significant but hidden structural damage? This sort of thing is much better known in the glider world, because every time a particular model reaches a set life the manufacturers buy one and very carefully dismantle it - wrecking it in the process, of course - to examine every part of the structure. Perhaps that will be worth doing to yachts if they ever start failing in significant numbers.

The point I was trying to make is that the visible damage occurs first and may not necessarily mean there is further unseen damage. It is also very difficult to repair cracked rib mouldings without it showing, so they are visible warning bells.

The thing that annoys me is that owners who run aground don't have the boat checked as almost certainly their insurance will cover the cost (or most of it). Ignoring it leads to situations like this where the seller has devalued his boat to the point that it is probably unsaleable.

 

[JumbleDuck]

I got tired of checking out Centaurs / Berwicks / Konsorts etc. to see if the work had been done ..

So many I saw were bodge DIY jobs and a number had to be cleared and redone. An awful job that gladly - yard guys did ...

The repair on mine was designed by Ian Nicolson, who called in every couple of days (the yard at Kilcreggan was just a couple of miles from his house) to check progress and advise. I did the headlining later. Horrible, horrible job.

 

[JumbleDuck]

The point I was trying to make is that the visible damage occurs first ...

If only it were that easy. However, as both the MCA and Pantaenius statements say, that's not a given.

The thing that annoys me is that owners who run aground don't have the boat checked as almost certainly their insurance will cover the cost (or most of it). Ignoring it leads to situations like this where the seller has devalued his boat to the point that it is probably unsaleable.

Agreed, sort of. The problem isn't that the seller has devalued his boat (he can do what he likes to it) but that he has contributed to the devaluing of everyone else's. Mind you, I regularly bounce off things but since I have 1.5 tonnes of lead surrounded by at least 1" of GRP it doesn't worry me too much.

 

[Ship'sCat]

If there are no cracks it's almost certainly fine. GRP is a very resilient material and we've yet to see boats reach the end of their service life due to GRP degradation. More often it's because owners have drilled into the GRP too many times, or done poor work on the boat, or left the boat to rot making it cost prohibitive to get back to useful.
What is it about the existing wachers you don't trust? 1968 is a very long time ago and they've held up just fine. If they're rusty then replace like for like, I can't see a reason to uprate something that's been in service for 53 years and coped with the loads.

The only place on the boat I have noticed cracking is very fine cracks around the rudder pintles - the rudder is fixed to the stern like a dinghy rudder. These cracks are like the cracks you see in old mugs or teapots.
As for the u-bolts, one of the bolts comes down so close to the bulkhead there isn't room for anything wider than the nut itself! And that is an original detail from 1968.

 

[Refueler]

The repair on mine was designed by Ian Nicolson, who called in every couple of days (the yard at Kilcreggan was just a couple of miles from his house) to check progress and advise. I did the headlining later. Horrible, horrible job.

Funny you mention Ian ... I have a bunch of his books ! Part of my 'collection' ...

I knew Phillip Bristow - he lived in the New Forest not too far from where I flew model aircraft .. actually my Father knew him first and I carried it over. I needed an old Bristows book and he gave me 1968 as it covered my boat ... later his son passed me the 1980 copy.

 

[JumbleDuck]

Funny you mention Ian ... I have a bunch of his books ! Part of my 'collection' ...

He's quite a character. I got him to do an insurance survey a couple of years ago and got just what I expected: a hand-typed report (using an actual typewriter) full of sensible suggestions.

 

[William_H]

Re cracking around the rudder attachments for a transom mounted rudder. I had similar concerns. I once had a little catamaran I had build of GRP. Fixed rudders. I loved to run it up on the beach. However caught a rock one day which ripped out the rudder attach along with a lump of GRP leaving a big hole. On present little boat the transom skin did seem to flex a bit. My access to inside the hull transom was aweful so I epoxied a few layers of carbon fibre to the outside and mounted the pintles through that and original holes. painted over it. Now a bit more robust.
Re OP question. Yes U bolt chain plates are a concern. Replace the U bolts if they are old. If the deck GRP appears to be solid. (when you tension up the rig) no worries assuming a decent sized washer to spread the load.
However belt and breaces fix is to fit a saddle to the under side of the U bolts. Get some stainless steel sheet say 30cms long by 20 cms wide in a semi triangle shape. The apex of the triangle is bent outwards and has a hole in it. Drill 12mm holes at random into the plate then epoxy the plate to the inside of hull at least 70cms below the chain plate. Lay up glass and epoxy over the plate and out across the hull. Holes in the plate aid in adhesion.
Get a small turn screw and link of wire to attach the saddle under the u bolt to the hull plate. Tension up the turn screw to take chain plate load.
Do the same for the inner stay chain plates or share the same embedded plate even if it not directly under the intermediate chain plates. The need for and dimensions of this load transfer system are entirely up to you depending on perceived loads and concern. ol'will

 

[Ship'sCat]

Re cracking around the rudder attachments for a transom mounted rudder. I had similar concerns. I once had a little catamaran I had build of GRP. Fixed rudders. I loved to run it up on the beach. However caught a rock one day which ripped out the rudder attach along with a lump of GRP leaving a big hole. On present little boat the transom skin did seem to flex a bit. My access to inside the hull transom was aweful so I epoxied a few layers of carbon fibre to the outside and mounted the pintles through that and original holes. painted over it. Now a bit more robust.
Re OP question. Yes U bolt chain plates are a concern. Replace the U bolts if they are old. If the deck GRP appears to be solid. (when you tension up the rig) no worries assuming a decent sized washer to spread the load.
However belt and breaces fix is to fit a saddle to the under side of the U bolts. Get some stainless steel sheet say 30cms long by 20 cms wide in a semi triangle shape. The apex of the triangle is bent outwards and has a hole in it. Drill 12mm holes at random into the plate then epoxy the plate to the inside of hull at least 70cms below the chain plate. Lay up glass and epoxy over the plate and out across the hull. Holes in the plate aid in adhesion.
Get a small turn screw and link of wire to attach the saddle under the u bolt to the hull plate. Tension up the turn screw to take chain plate load.
Do the same for the inner stay chain plates or share the same embedded plate even if it not directly under the intermediate chain plates. The need for and dimensions of this load transfer system are entirely up to you depending on perceived loads and concern. ol'will

Thanks, that's interesting.

 

[Laminar Flow]

On GRP ageing: after 1,000,000 (million) stress cycles, the strength of the laminate is reduced by half - a fair argument for increasing laminate thickness in boats intended for long distance voyaging.

A keel grid system should (and can) be designed to sustain a grounding at hull speed. The loads are entirely calculable. ABS offers specific scantling rules as a guide for appropriate design. Larsson & Eliasson dedicate an entire chapter to the problem; if someone is interested in the specifics.
In this respect grid or keel attachment failure is either attributable to poor engineering or bad construction or both.

On the frequency of groundings: I had a long chat with a local salvage operator who complained bitterly to me that GPS and plotters had ruined his business. In this respect it could be argued that either there are fewer boats out and about or that the number of accidental groundings has come down due to better navigational aids.
If, as Tranona claims, a lot of the yards are still kept busy making expensive repairs post grounding, then one might assume that Pantanius and the MRC are on to something and, consequently, there is something very wrong with the way keels are currently attached.
I think grounding is a fairly regular occurrence, particularly when cruising in areas with thin water. The Waddenzee and the Baltic come to mind, the latter also has a goodly amount of uncharted rocks to offer. Any serious boat should be designed and built to withstand such an impact.